Stress limiting hoist

ABSTRACT

A hoist motor operates a hoist load shaft through an overload clutch having a circular gear that is in frictional relation to a disc member for applying a predetermined amount of torque for lifting a load, and slipping when there is overload. The disc member is mounted through screw threads on the load shaft and pressing the member against a shoulder to transmit the predetermined torque in load lifting direction. The screw threads have a limited length in axial direction that causes them in effect to disengage when the hoist motor rotates the disc in load lowering direction. The clutch cannot then apply the predetermined torque but a spring presses end portions of the threads against each other so as to transmit torque that is limited to a small amount, much less than the frictional surfaces of the clutch would accept. The load shaft operates a load chain having a limit member that strikes a stop surface on the hoist frame to limit lowering movement of the hoist. The hoist stress that is due to the small amount of lowering torque, when added to the considerable stress that may be due to a load when the chain limit member strikes the stop surface of the hoist, will be insufficient to overstress parts of the hoist.

United States Patent [191 Dahl Oct. 12, 1971 US. Cl 254/168, 64/30 R,64/30 A,

Int. Cl. F16d 7/02, B66d l/12 Field of Search 254/168; 64/30 R, 64/30 A;192/56 R, 56 C, 150, 94

References Cited UNITED STATES PATENTS 5/1927 Starkey 192/56 C 10/1951Metcalf et al 254/168 6/1941 Schroeder 254/ 168 10/1947 Nelles 254/168 X10/1952 Launder 192/56 C X 9/1959 Digby 64/30 A X Primary Examiner-AllanD. Herrmann Attorney--E. B. Brownson 111 3,741,527 June 26, 1973 [5 7]ABSTRACT A hoist motor operates a hoist load shaft through an overloadclutch having a circular gear that is in frictional relation to a discmember for applying a predetermined amount of torque for lifting a load,and slipping when there is overload. The disc member is mounted throughscrew threads on the load shaft and pressing the member against ashoulder to transmit the predetermined torque in load lifting direction.The

screw threads have a limited length in axial direction that causes themin effect to disengage when the hoist motor rotates the disc in loadlowering direction. The clutch cannot then apply the predeterminedtorque but a spring presses end portions of the threads against eachother so as to transmit torque that is limited to a small amount, muchless than the frictional surfaces of the clutch would accept. The loadshaft operates a load chain having a limit member that strikes a stopsurface on the hoist frame to limit lowering movement of the hoist. Thehoist stress that is due to the small amount of lowering torque, whenadded to the considerable stress that may be due to a load when thechain limit member strikes the stop surface of the hoist, will beinsufficient to overstress parts of the hoist.

10 Claims, 2 Drawing Figures PATENIEU JIIIZS I973 SHEU 2 [IF 2 l STRESSLIMITING HOIST FIELD OF INVENTION The novel hoist of my invention is ofthe kind having a motor driven operating shaft that applies torque inopposed directions effecting rotation of a load shaft for lifting andlowering a load. My hoist particularly will limit the stresses that maybe due to torque that the motor applies in. either direction.

BACKGROUND OF INVENTION As will be appreciated by those skilled in theart, hoists frequently are abused by attempts of an operator to utilizethe hoist for lifting a load that weighs more than the safe capacity ofthe hoist, causing stresses that are injurious to the hoist and that area source of danger to persons near .the hoist. Therefore, designersworking in the art have conceived various hoists that will limit theamount of load to be lifted, sometimes requiring electrical circuits andequipment for stopping operation of the hoist motor when the hoist isoverloaded. One of the more satisfactory types of construction utilizesa torque limiting clutch that will yield when there is an attempt tolift a load that is excessive. In fact, the hoist designed by Suez andSmith and shown by their US. Pat. application Ser. No. 155,979 comprisesa torque limiting clutch that acts to extremely good effect underconditions of overload. However, so far as I am aware, there does notexist in the prior art a hoist in which a torque limiting clutch will befully effective to control stresses to which the hoist may be sufjectedwhen the hoist moves in a lowering direction.

In theory, a hoist motor need apply no power in order to lower a load.In practice, the motor in hoists of the particular kind does act toeffect operation of the hoist in lowering direction, it being necessaryto apply a small amount of power in order to overcome friction betweenparts of the hoist and to control the lowering movements of the loadmember of the hoist. If the hoist 'motor, when acting in loweringdirection, can apply the amount of power that it applies in liftingdirection, the power is excessive and tends to cause stresses thatactually are unnecessary. Those stresses may reach a considerablemagnitude when, as may happen, apart of the hoist meets an obstructionto its lowering movement. I now contribute by my invention a novel hoistthat will place a low limit on the stresses that may be incidental to alowering movement of the hoist, while also being effective to limit to apredetermined amount the stresses that the hoist need accept whenoperating in load lifting direction.

SUMMARY OF THE INVENTION In the hoist of my invention, I connect atorque limiting'clutch between an operating shaft and a load shaft ofthe hoist, said clutch comprising parts movable to a position that iseffective to apply a predetermined amount of torque between theoperating shaft and the load shaft, and to a further position that'isineffective to apply said predetermined amount of torque while theoperating shaft rotates in that position.

The torque limiting clutch of my hoist may utilize parts that arefrictionally related, one part being a circular gear meshing with oneshaft, and having a tapered opening in spring pressed frictionalrelation to a tapered surface on a disc member that is mounted onanother shaft. As a feature of my invention, the disc member can move inaxial direction so as to place the torque limiting clutch in positionsthat will accept differing amounts of torque relatively to its shaft.

As a preferred feature, I mount the torque limiting clutch to rotate onscrew threads whereby to move between a load lifting position and a loadlowering position on a shaft, the screw threads being formed so as tosubstantially'disengage whereby the clutch while in its load liftingposition may rotate relatively to the shaft. As a particular feature ofthis part of my invention, my hoist has spring means that press endportions of the screw threads against each other so as to apply a degreeof torque between the clutch and its shaft while the clutch rotates inits load lowering position.

A further feature of my invention resides in stop means that will engagepositively to limit lifting and lowering movements of a hoist loadmember, in combination with stress limiting means that will effectivelylimit the stresses that are incidental to the limiting effect of thestop means in either direction. More particularly, the stress limitingmeans will limit to a relatively small amount the stresses that are dueto engagement of the stop means while the hoist motor acts in loweringdirection.

I have thus outlined rather broadly the more important features of myinvention in order that the detailed description thereof that followsmay be better understood, and in order that my contribution to the artmay be better appreciated. There are, of course, additional features ofmy invention that will be described hereinafter and which will form thesubject of the claims appended hereto. Those skilled'in the art willappreciate that the conception on which my disclosure is based mayreadily be utilized as a basis for the designing of other structures forcarrying out the several purposes of my invention. It is important,therefore, that the clims be regarded as including such equivalentconstructions as do not depart from the spirit and scope of myinvention, in order to prevent the appropriation of my invention bythose skilled in the art.

DESCRIPTION In the drawings:

FIG. 1 shows a plan view, partly in section, of a hoist that utilizes myinvention.

FIG. 2 shows an end view, partly in section on the line 2-2 in FIG. 1.

Referring now more particularly to FIG. 1 of the drawings, 1 show myhoist 10 equipped with a rather .usual hoist motor 11 and motor brake 12that are mounted on opposed ends of a hoist frame 13. Connecting themotor 11 and brake 12 is a drive shaft 14 extending through a hollowload shaft 15. A gear portion 16 on shaft 14 meshes with a gear 17 thatis keyed to an operating shaft 18 so that motor 11 will rotate thatshaft, each of the shafts being mounted through suitable bearings torotate on hoist frame 13. I believe it will be unnecessary to describein detail the functional relation between motor 11 and brake 12 becausethat relation is quite conventional, and I shall merely indicate thatbrake 12 is so controlled automatically as to permit drive shaft 14 torotate when motor 11 is energized, and oppose rotation when the motor isnot energized.

In the novel concept of my invention, the operating shaft 18 and loadshaft 15 are connected through a torque limiting clutch, indicatedgenerally by the numeral 20 in FIG. 1. Clutch 20 includes a circulargear 21 meshing with a pinion 22 that is formed on the operating shaft18, and an inner disc member 23 that is mounted through screw threads24, 25 coacting on member 23 and load shaft 15. The peripheral surfaceof disc member 23 and the opening of circular gear 21 have a shape thatis tapered, and friction material 26 is interposed so as to offerfrictional surfaces engaging between gear 21 and member 23. One or morespring discs 27 are held by a retaining ring 28 on a hub portion of discmember 23 and press against circular gear 21 so as to hold the gear andmember in frictional engagement. The disc member 23 then will accept apredetermined amount of torque that may be applied through rotation ofthe operating shaft 18, while an excessive amount of torque will beabsorbed by frictional slippage.

As shown in FIG. 1, the load shaft has a shoulder 29 forming stop meansfor the disc member 23. Also, the screw threads 24, 25 are so inclinedthat the disc member 23 when rotating in load lifting direction willpress against shoulder 29, forming a positive connection so that thetorque limiting clutch then is in position to apply its predeterminedamount'of torque to load shaft 15. When rotating in direction to lower aload, disc member 23 naturally will move on screw threads 24, away fromshoulder 29, or toward the right as viewed in FIG. 1.

I call attention to the fact that screw threads 24, 25 have a relativelylimited length in axial direction, such that they will substantiallydisengage to terminate their screw action when disc member 23 continuesto rotate in load lowering direction. The torque limiting clutch 20 thenis in a further position that may be termed a load lowering position, inwhich disc 23 rotates while end portions 33, 34 of the screw threads 24,25 remain in contact with each other. I particularly hold the thread endportions 33, 34 in contacting relation, utilizing for the purpose aspring plate 30 mounted on the hoist frame, as by screws 31. That plate30 has a series of spring fingers 32 pressing against the torquelimiting clutch 20 or its spring discs 27 while the clutch is in itsload lowering position. The pressure applied by spring fingers 32 willbe accepted between the end portions 33, 34 of the screw threads,causing the disc member 23 to apply a small amount of torque in loadlowering direction to the load shaft 15. The torque that can be soapplied will be limited and much less than the predetermined amount thatcan be applied through the frictional relation between disc member 23and gear 21. It may be mentioned here that the spring pressure appliedby spring fingers 32 also will cause screw threads 24, 25 to engagefully so that the clutch 20 will move to its load lifting positionagainst the shoulder 29 when disc member 23 rotates in load liftingdirection.

It will thus be seen that the torque limiting clutch 20 will move to aload lowering position in which the hoist motor can cause no more than asmall amount of stress in the hoist, and also to a load lifting positionin which the motor may cause a limited but larger amount of stress thatis necessary for lifting a predetermined load.

I shall now refer to FIG. 2 to describe the manner in which the torquelimiting features of my invention will act in relation to a hoist loadmember. For the purpose of description, I show a load chain 36 formingthe load member and engaging a chain sheave 35 formed on the load shaft15 (FIG. 1), as is quite usual in the art. Chain 36 is equipped with aload hook 37 for engaging a load while the hoist is supported through ahook 38 on the hoist frame 13, and the chain has a slack portion 39secured at 40 to frame 13. To limit the lifting and lowering movementsof load chain 36, as is necessary, I show an extremely simplearrangement in which lifting limit and lowering limit members 41, 42 aresecured to appropriate points on chain 36 and its slack portion 39 forengaging a stop portion on frame 13. Due to the action of torquelimiting clutch 20, as I have described, it will be understood that amovement of lifting limit member 41 against stop portion 43 will causeno more than a predetermined amount of stresses in the hoist and itschain 36.

To understand stresses that are incidental to lowering operation of thehoist motor, let us assume first that the hook 37 supports a load. Whilethe chain 36 moves in lowering direction, its stresses will. besubstantially those that are due to the load. Now consider that thechain 36 reaches its lower limit position, in which the slack chainportion 39 is in its dotted line position 39a and limit member 42 is inits position 42a against the frame stop portion 43. In the position 42aof limit member 42, the limit member will accept the load, thus causingthe stress that is due to the load to be applied to that part 44 of thechain that extends between chain sheave 35 and member 42. That stressmay be ofa large magnitude, and it then is important that no greatamount of stress be added to the chain part 44.

It will be remembered that my torque limiting clutch 20 will apply verylittle torque in load lowering direction to the load shaft 15.Therefore, should the hoist motor continue to operate while chain 36 isin its lower limit position, chain sheave 35 will add merely a smallamount of stress to that which the load causes in the part 44 of thechain. Thus, it is possible through the concept of my invention toutilize extremely simple and positive stop means to limit loweringmovements as well as the lifting movements of a hoist load member, whileeffectively limiting the stresses that may be due to the operation ofthe stop means.

I believe that the construction and the operation of my novel stresslimiting hoist now will be understood, and that persons who are skilledin the art will fully appreciate that I have made a contribution of veryconsiderable value to the hoist industry.

I claim:

1. In a hoist having a load shaft, a load member connected to the loadshaft, and a motor driven operating shaft rotatable in opposeddirections effecting rotation of the load shaft whereby to lift and tolower a load supported on the load member, a torque limiting clutchconnected between said shafts, said torque limiting clutch beinglongitudinally movable between said shafts to a first postion that iseffective to engage said clutch with one of said shafts to apply apredetermined amount of torque between the operating shaft and the loadshaft, and to a second position that is effective to disengage saidclutch to make said clutch ineffective to apply said predeterminedamount of torque to said load shaft while allowing the operating shaftto rotate, and means for longitudinally moving said clutch to said firstand second position in response to load lifting and load loweringrotation of said operating shaft so as to place differing limits on thehoist stresses that the operating shaft may cause through the loadshaft.

2. The combination set forth in claim 1 in which there are means actingin response to the operating shaft torque to move said clutch mentionedto said first-mentioned position when the torque is in load liftingdirection and to said further position when the torque is in loadlowering direction.

3. The combination set forth in claim 2, including a lifting limitmember secured in position on said load member to engage a stop portionon the hoist so as to limit positively the extent of lifting movement ofthe hoist, said torque limiting clutch being effective to limit to asmall amount the hoist stresses that are due to the applied torque whensaid limit member engages said stop portion.

4. In a hoist having a load shaft, aload member connected to the loadshaft, and a motor driven operating g shaft rotatable in opposeddirections effecting rotation of the load shaft whereby to lift and tolower a load supported on the load member, a torque limiting clutchconnected between said shafts, said torque limiting clutch comprisingparts movable to a position that is effective to apply a predeterminedamount of torque between the operating shaft and the load shaft, and toa second position that is ineffective to apply said predetermined amountof torque to said load shaft while the operating shaft rotates, meansfor moving said clutch parts to said first and second positions so as toplace differing limits on the hoist stresses that the operating shaftmay cause through the load shaft, means acting in response to theoperating shaft torque to move said clutch parts to said first positionwhen the torque is in load lifting direction and to said second positionwhen the torque is in load lowering direction, said torque lim itingclutch having parts that are frictionally related through surfacesengaging to accept said predetermined amount of torque, one of saidparts being mounted for rotation relatively to one of said operating andload shafts, and there being means locking said one of the parts so asto rotate with said one of the shafts when the parts of the clutch moveto their first position.

5. The combination set forth in claim 4 in which the means that move theclutch parts have portions that are in a rotatable relation enabling theclutch parts to remain in their further position while said one of theparts rotates relatively to said one shaft.

6. The combination set forth in claim 4 in which the means that move theparts of said torque limiting clutch comrises screw threads engagingbetween said one clutch-part and one shaft, stop means against which thethreads move said one part on said one shaft when moving the clutchparts to their first-mentioned position, and end portions of said screwthreads in opposed relation to each other when the clutch parts are intheir further position and enabling the parts to remain in that positionwhile said one part rotates in lowering direction relatively to said oneshaft.

7. The combination set forth in claim 6 including a lifting limit membersecured in position on said load member to engage a stop portion on thehoist so as to limit positively the extent of lifting movement of thehoist, said torque limiting clutch being effective to limit to a smallamount the hoist stresses that are due to the applied torque when saidlimit member engages said stop portion.

8. In a hoist having a load shaft, a load member connected to the loadshaft, and a motor driven operating shaft rotatable in opposeddirections effecting rotation of the load shaft whereby to lift and tolower a load supported on the load member, a clutch longitudinallymovable between said shafts to a first and a second position in responseto load lifting and load lowering rotation of said operating shaft,means for moving said clutch to said first position to apply apredetermined amount of operating shaft torque in load lifting directionto the load shaft, said clutch yielding in said first position when thetorque is greater than said predetermined torque, and means for movingsaid clutch to said second position to apply a relatively small amountof the operating shaft torque in load lowering direction to the loadshaft, said clutch yielding in said second position when the amount oftorque is less than said predetermined amount.

9. A combination set forth in claim 8 including lifting and loweringlimit members secured in positions on said load member to engage a stopportion on the hoist so as to limit positively the extent of lifting andlowering movements of the hoist, while the means that apply torque inlifting and lowering directions yield.

10. The combination set forth in claim 9 in which the load member is aflexible member such as a chain engaging a wheel on the load shaft, saidflexible member having at opposed sides of the wheel a load portion anda slack portion to which said lifting and lowering limit members aresecured, the slack portion of the flexible member being stressed by aload on said load portion of the member when the lowering limit memberengages the stop portion of the hoist, and said means that apply torquein load lowering direction limiting to a relatively small amount thestresses that an operation of the motor driven shaft can add to saidstressing of the slack portion of the flexible member.

ll I t

1. In a hoist having a load shaft, a load member connected to the loadshaft, and a motor driven operating shaft rotatable in opposeddirections effecting rotation of the load shaft whereby to lift and tolower a load supported on the load member, a torque limiting clutchconnected between said shafts, said torque limiting clutch beinglongitudinally movable between said shafts to a first postion that iseffective to engage said clutch with one of said shafts to apply apredetermined amount of torque between the operating shaft and the loadshaft, and to a second position that is effective to disengage saidclutch to make said clutch ineffective to apply said predeterminedamount of torque to said load shaft while allowing the operating shaftto rotate, and means for longitudinally moving said clutch to said firstand second position in response to load lifting and load loweringrotation of said operating shaft so as to place differing limits on thehoist stresses that the operating shaft may cause through the loadshaft.
 2. The combination set forth in claim 1 in which there are meansacting in response to the operating shaft torque to move said clutchmentioned to said first-mentioned position when the torque is in loadlifting direction and to said further position when the torque is inload lowering direction.
 3. The combination set forth in claim 2,including a lifting limit member secuRed in position on said load memberto engage a stop portion on the hoist so as to limit positively theextent of lifting movement of the hoist, said torque limiting clutchbeing effective to limit to a small amount the hoist stresses that aredue to the applied torque when said limit member engages said stopportion.
 4. In a hoist having a load shaft, a load member connected tothe load shaft, and a motor driven operating g shaft rotatable inopposed directions effecting rotation of the load shaft whereby to liftand to lower a load supported on the load member, a torque limitingclutch connected between said shafts, said torque limiting clutchcomprising parts movable to a position that is effective to apply apredetermined amount of torque between the operating shaft and the loadshaft, and to a second position that is ineffective to apply saidpredetermined amount of torque to said load shaft while the operatingshaft rotates, means for moving said clutch parts to said first andsecond positions so as to place differing limits on the hoist stressesthat the operating shaft may cause through the load shaft, means actingin response to the operating shaft torque to move said clutch parts tosaid first position when the torque is in load lifting direction and tosaid second position when the torque is in load lowering direction, saidtorque limiting clutch having parts that are frictionally relatedthrough surfaces engaging to accept said predetermined amount of torque,one of said parts being mounted for rotation relatively to one of saidoperating and load shafts, and there being means locking said one of theparts so as to rotate with said one of the shafts when the parts of theclutch move to their first position.
 5. The combination set forth inclaim 4 in which the means that move the clutch parts have portions thatare in a rotatable relation enabling the clutch parts to remain in theirfurther position while said one of the parts rotates relatively to saidone shaft.
 6. The combination set forth in claim 4 in which the meansthat move the parts of said torque limiting clutch comrises screwthreads engaging between said one clutch part and one shaft, stop meansagainst which the threads move said one part on said one shaft whenmoving the clutch parts to their first-mentioned position, and endportions of said screw threads in opposed relation to each other whenthe clutch parts are in their further position and enabling the parts toremain in that position while said one part rotates in loweringdirection relatively to said one shaft.
 7. The combination set forth inclaim 6 including a lifting limit member secured in position on saidload member to engage a stop portion on the hoist so as to limitpositively the extent of lifting movement of the hoist, said torquelimiting clutch being effective to limit to a small amount the hoiststresses that are due to the applied torque when said limit memberengages said stop portion.
 8. In a hoist having a load shaft, a loadmember connected to the load shaft, and a motor driven operating shaftrotatable in opposed directions effecting rotation of the load shaftwhereby to lift and to lower a load supported on the load member, aclutch longitudinally movable between said shafts to a first and asecond position in response to load lifting and load lowering rotationof said operating shaft, means for moving said clutch to said firstposition to apply a predetermined amount of operating shaft torque inload lifting direction to the load shaft, said clutch yielding in saidfirst position when the torque is greater than said predeterminedtorque, and means for moving said clutch to said second position toapply a relatively small amount of the operating shaft torque in loadlowering direction to the load shaft, said clutch yielding in saidsecond position when the amount of torque is less than saidpredetermined amount.
 9. A combination set forth in claim 8 includinglifting and lowering limit members secured in positionS on said loadmember to engage a stop portion on the hoist so as to limit positivelythe extent of lifting and lowering movements of the hoist, while themeans that apply torque in lifting and lowering directions yield. 10.The combination set forth in claim 9 in which the load member is aflexible member such as a chain engaging a wheel on the load shaft, saidflexible member having at opposed sides of the wheel a load portion anda slack portion to which said lifting and lowering limit members aresecured, the slack portion of the flexible member being stressed by aload on said load portion of the member when the lowering limit memberengages the stop portion of the hoist, and said means that apply torquein load lowering direction limiting to a relatively small amount thestresses that an operation of the motor driven shaft can add to saidstressing of the slack portion of the flexible member.